The present invention relates to a novel composition based on high molecular weight water-soluble acrylamide copolymers for sizing textile yarns (or fibres). The invention applies particularly well to the sizing of natural fibres, particularly of the cotton type, optionally in the presence of artificial fibres, in particular polyester.
In the textile industry, during weaving operations, the yarns or fibres are subjected to repeated stretching. Yarn stretching can cause breakage. The elongation capacity of the yarn. must therefore be exploited, depending on its type.
In addition to the stretching, other stresses exist. These are essentially:                abrasion: action of wear by friction. This causes hairiness of the yarns, pilling due to friction against various parts (heddles, comb teeth, etc.); and        hairiness: the tendancy of the fibre ends to separate from the spun yarn body. This can cause interyarn couplings which give rise to yarn breakage or insertion defects by the weft vector.        
The use of sizing products is known to protect yarns against these damaging forces and to improve their strength.
To obtain good results, the size must be selected taking account of the following properties:                break strength and elongation at break,        flexibility of the size film which must match the elongations undergone by the yarn,        good adhesion to the yarn,        appropriate viscosity which depends on the yarns, however, an excessively high viscosity can cause difficulties in case of interruption on the sizing machine.        
Moreover, the sizing must not damage the yarn and the liquor must comprise compatible products exclusively. Furthermore, the comb must not be subject to size deposits which, by hardening, could act as abrasives on the yarns.
It should be noted that sizing is an intermediate finish, which is removed after the weaving operation. This operation precedes the finishing of the fabric, after which the size is completely removed. This may prove to be very pollutant because of the releases generated. It is therefore advantageous to have a product which has good solubility for desizing.
Conversely, documents EP-A-262 945 and U.S. Pat. No. 6,736,865 describe products for treating not individualized yarns, but finished woven textiles.
Document EP-A-262 945 thus describes a product combining an acrylamide polymer in the presence of other types of polymers for fastening colour to the previously woven fabric.
Document U.S. Pat. No. 6,736,865 describes a product based on acrylamide in the presence of other components for treating finished textiles to confer crease resistance and dimensional stability, particularly at the time of colour fastening.
In the paper field, document JP 60258244 describes the possibility of making a sheet water-repellent during formation, by treating the paper (and not textile) fibres using a mixture of a cetene and an acrylamide polymer.
The choice of the size mainly depends on the type of chain, and also taking account of the type of weaving:                dry weaving: rapier, projectile, airjet looms,        hydraulic weaving: water jet looms which require products unaffected by water in the weaving conditions.        
The main types of basic products usable as sizing agents are natural or synthetic polymers, which are classed as follows:                starches: varieties of starch,        starch derivatives: ethers, acetates,        cellulose derivatives: carbOXYmethyl, methyl and ethyl cellulose,        polyvinyl alcohol and vinyl acetate copolymers, polyesters,        acrylics; these are mainly suitable for synthetic and artificial yarns;        
however, they are also found in combination with starches or cellulose derivatives for natural fibres and mixtures thereof.
Sizing agents of the acrylic type are obtained by homopolYmerization or copolymerization of various derivatives of acrylic acid or methacrylic acid with other monomers such as styrene, vinyl acetate, acrylamide, etc. By an appropriate choice and dosage of the monomers, synthesis produces macromolecular substances, whereof the physical properties can be varied in a very wide interval. This explains the many sizing applications of various yarns: polyamide, polyester, cellulose. The main properties which they provide are:                excellent interstrand cohesion capacity,        high performance on dry looms.        
However, many constraints apply concerning the use of the abovementioned sizing agents. In particular, they are often associated with the quantities required for these sizes to be effective, and with their low activity when used alone on natural fibres.
The problem faced is therefore to find a novel sizing product for sizing natural and/or artificial fibres on dry looms, and which meets the requirements of the industry, that is:                good affinity for yarns or fibres,        easy implementation (sizing speed, etc.),        improved loom productivity: higher yarn or fibre strength, while limiting comb fouling,        easy and non-pollutant removal with water, and        in addition, significantly reduce the quantities of sizing agent and hence the total cost of the operation,        